How can I insert values at the start of an array of vectors in Blender 2.8 using Python
By default Vertices vectors are in 3 dimensions so we need to create a new one with 4 dimensions.

import bpy
from mathutils import Vector

try:
    vectors = [Vector((7.0, v.co.x, v.co.y, v.co.z)) for v in bpy.context.object.data.vertices]    
    print(vectors)
except AttributeError:
    print('Please select a mesh object')


Result :